Quitting cannabis use improves cognition in people with schizophrenia

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​CAMH study’s findings
may point to a new approach to benefit the high proportion of people with
schizophrenia who also have a cannabis use disorder

TORONTO, June 29, 2017 - A new CAMH study suggests that quitting cannabis
substantially improved an important aspect of cognition in people with
schizophrenia who were chronic cannabis users. Published in April 2017 in Neuropsychopharmacology, it’s the
first study to investigate how abstaining from cannabis use for one month impacts
cognition or thinking processes in this population.

About one in every 100 people has schizophrenia, a complex
and severe mental illness. People with schizophrenia may experience impairments
in cognition that profoundly affect everyday living, says Dr.
Tony George, senior author of the study and Chief of CAMH’s Addiction
Division. Cognition refers to the thinking processes involved in learning,
memory and applying knowledge.

Dr. Tony George

High rates of cannabis use among people with schizophrenia and
poor outcomes related to its use interested the research team in studying how cannabis
abstinence alters cognition, says Dr. George. While about three per cent of the
general population has a cannabis use disorder, the rate soars dramatically in
people with schizophrenia – it’s estimated that about 25 per cent of people
with schizophrenia also have a cannabis use disorder.

The preliminary study, led by Dr. Rachel Rabin while
completing her Ph.D. studies, looked at how quitting cannabis use for 28 days
affected several areas of cognition, including verbal learning and memory, attention,
impulsive behaviours and motor function. A total of 19 people with
schizophrenia and a comparison group of 20 people without a mental illness, all
of whom had cannabis dependence, attempted to abstain from cannabis use for the
full study period. In people with schizophrenia, the area called verbal
learning and memory improved significantly – by 40 per cent by the study’s end.

“In people with schizophrenia, our research showed that if
you can abstain, you will see better outcomes in a key area of cognition,” says
Dr. George, who also heads the Biobehavioural Addictions and Concurrent
Disorders Research Laboratory in CAMH’s Campbell
Family Mental Health Research Institute, and is Professor of Psychiatry at
the University of Toronto.

Verbal learning and memory is the ability to understand and
recall what we’ve heard, and it’s vital to everyday living, allowing us to
remember a conversation, directions or other information that people share
orally. In earlier research, it’s also been shown to be impaired in both people
with schizophrenia and individuals with cannabis use disorder. Improving verbal
learning and memory could make a marked difference in a person’s life, such as
helping a person to succeed in the workplace, says Dr. George.

Ranging from ages 18 to 55, participants were asked to quit
using cannabis for 28 consecutive days, the period needed for this long-acting
substance to be fully out of a person’s body, and received counselling to help
manage withdrawal symptoms and cravings. By the end of 28 days, eight of 19 people
with schizophrenia and 11 of 20 people from the comparison group had abstained
from cannabis use for the full study period. “These abstinence rates illustrate
the difficulties that people frequently experience when attempting to quit
chronic cannabis use,” says Dr. George.

Researchers assessed different aspects of cognition during
and at the end of the study. While verbal learning and memory improved
significantly in people with schizophrenia, people in the comparison group
experienced only a minor improvement, which supports early findings that people
with schizophrenia may be more susceptible to the effects of cannabis use.

“As we approach cannabis legalization in Canada, our study
provides further evidence that, in people with mental illness, cannabis use
warrants caution,” says Dr. George. The research team will look to investigate cannabis
abstinence further in this population in a larger sample.

The study was supported by the Canadian Institutes of Health
Research, the Brain and Behavior Research Foundation and the Chair in Addiction
Psychiatry at the University of Toronto.

Given the challenges associated with quitting chronic
cannabis use, Dr. George and CAMH Scientist Dr. Mera Barr are both leading
studies using a novel, non-invasive brain stimulation treatment, called
repetitive transcranial magnetic stimulation (rTMS). “There are no medications
to treat cannabis use disorder – the only treatments are behavioural therapies provided
by a health-care professional,” says Dr. George. “Our goal is to determine if
brain stimulation can help reduce the cravings people have when they experience
cannabis withdrawal, which play a big role in people relapsing.” In an earlier
study, Dr. George showed that rTMS
reduced cigarette cravings in smokers with schizophrenia.

The Centre for Addiction and Mental Health
(CAMH) is Canada’s largest mental health and addiction teaching hospital
and a world-leading research centre in this field. CAMH combines
clinical care, research, education, policy development and health
promotion to help transform the lives of people affected by mental
illness and addiction. CAMH is fully affiliated with the University of
Toronto, and is a Pan American Health Organization/World Health
Organization Collaborating Centre. For more information, please follow @CAMHnews or @CAMHResearch on Twitter.